Let the number of students in the class be n, then the total score of the class for the first time is 85.13 * n;

The second time, I knew that Wujiang's score was 9 points less, so the total score of the whole class was 85. 13*N+9 points;

So (85.13 * n+9)/n = 85.31,so N=50 people.